Dalilean

Have you ever had one of those moments when thinking about different, seemingly unrelated ideas suddenly add up?

I have read a lot of the discutions about the advantage the standard airbox intake our cars' have and how open air intakes do little else than a louder engine. I have even read about how dyno results prove this. I thought this was in part because the end nose of the was coned foward, taking in speeding air. That's till I looked at the boxes end.

On the same note I have been talking with some of my "ricer" friends (turbo modified car owner's) about the advantages of force induction. This is basically forcing air into the engine, maximizing the intake of the engine.

Add to this the fact that I was considering making a NACA duct to ventilate the interior of the AC deleted car, the faster I would go, the more air the car would get.

That's when it hit me. This is nothing new! A ram air intake! I have seen and read about these. The faster you go, the more air is FORCED into the intake. Sure this thing would do little on a stationary car, but on a car going at high speeds...
Sure, dyno results would show little, if any improvements. I could actually show a decrees in performance! Remember, a dyno is a stationary test. At high speeds conditions are different. This becomes a "natural" charger!

Most "ram air intakes" for ricers are not real ram airs. These are just cone filters set-ups. I am talking about Impala style ram airs, where an intake box (separating the intake from the rest of the engine) opens through scoop or the grill, where all the air that is force in while driving has nowhere else to go but into the intake.

Has anyone made a ram air for the 944?
What improvement does it have?
How could one test these improvements, on a non stationary enviroment?

OriginalSterm

Ram Air is a misconception. Cars such as the Firebird with "Ram Air" is just a fancy cool air intake. To actually Force air into the intake from vehicle speed, you need to be approaching the speed of sound. Otherwise, you don't actually cram any more air in.

Do a search of ram air, someone posted a link to a corvette forum where an expert explains this much better.

bader$

I have heard that there is really no benefit to ram air except where air is drawn from the low pressure area of the windshield/cowl area, and only then because the air is calm and cool.

Adam Richman

FWIW, Ram air doesn't occur below something in the high 200 mph range (want to say its a particular airspeed but I would guess altitude plays a part). You cannot physically "force" air into an intake outside of forced induction at any attainable road car speed. The value of the intakes that leave the engine bay (both above and below) are that they take in cooler air charge which is more dense - I would work toward that goal not attempting to create the mythical "ram air." A NACA duct will not compact air, it simply redirects air well building momentum. This is the same thing as the guys that take a 5" inlet down to a 3" outlet for brake ducts thinking it "speeds" up the air - w/out a fan or motor, it does not, it just restricts the 5" opening to only allow 3" of air in. Besides, in how I understand ram air to have to function, it needs to open larger as it heads toward the TB not get smaller.

Blue S2

The S2 beat ya to it. Porsche put the intake inside the front bumper outside of the engine bay. Changing the filter is a P.I.T.A.

Chaging from a box to a cone would basically make the situation you are saying. Assuming you are moving though, and air is readily being inhaled... how much MORE air could you get? I would think the restrictions lie elsewhere.

Sasquatch

Guys, slow down a bit. Ram air is used very frequently on sport bikes with great success. I hated dyno tuning ram air bikes on a dyno because I could never force enough air to simulate 90mph into the air intakes with fans. I could only use educated guesses then take the bike out and ride it.

Ram air works. It works well. On a 1 liter superbike, you can gain 7-10 mph top speed with ram air. For giggles, when I first started tuning modern superbikes I took a zx 7 and covered the ram air intakes and popped the tubes off in the fairings so it would still get nice and cool air, but no ram air. What a huge difference. The bike literally ran like crap when I jumped on the throttle at 60mph. It would pop, wheze and sputter. Hook the ram back up and it would take off like a rocket.

Before you start saying that it was a lot smaller displacement motor, take into consideration a zx-11 is running at near 5500 rpms at 70mph. Now that is like a 2.2liter motor running at 2750 rpms. So they are alot closer in actual cfm consumption than you think.

Now, you are not actually pressurizing the intake track by using ram air, but just reducing the vacuum. It has the same effect, just at a lesser degree. Going from 12 inches of mercury vacuum to 10 inches with ram air is like adding 1 psi boost to a turbo. Not much, but noticeable. (2.03 in/merc = 1psi)

2.5 liter motor @ 3,000 rpm (60mph+/-) = 53.0217cfm going through the motor.

You would need a fairly decent size scoop to offset this. But it is possible.

joseph mitro

i tried putting a 924 turbo header panel on my car, essentially creating "ram air" because my airbox intake comes from under the header panel similar to the S2. it did nothing except let water in during heavy rainstorms and cause the engine to stumble (probably because the rubber seal under the header panel was deteriorating and the distributor was getting wet). i sold the 931 header panel within two months.

Adam Richman

If you were physically forcing air into the intake w/ a fan, that's neither simulating the real world or "ram air." I don't believe your idea of a "scoop" is correct for creating ram air - think its backwards. I don't doubt you could approach 1 atmosphere by modifying a naturally aspirated intake but you will not exceed it on terra firma in a street legal car from everyone I spoke with until you either a.) exceed whatever that speed is (and its much greater than 90mph) or b.) compact the air via forced induction.

Now we took off my long intake on the dyno to see what happened (actually it was cause we left if off ) and saw a 4 whp drop in doing so. But I'd bet that has much more to do w/ length, air temp, etc ... that wasn't the effect of the fan blowing across it creating force. Perhaps akin to your covering of the ferring intake holes.

Danno

A lot of the sport-bike improvements have been through engine designs as well. Just because someone comes up with a 7-10mph increase in top-speed through various mods, doesn't mean it's all attributed to the ram-air. Another manufacturer will come up with similar gains without any ram-air at all.

You also gotta take a look at the intake-system, from outside air to the cars, it's maybe 2-feet maximum on a bike. Ram-air may work with that short of an intake. Try the 6-feet or so on our cars along with the restrictive AFM and I doubt you see any gains at all.

Mongo

I think ram-air may have some effect of pushing more air into the intake, however, there is still restriction due to the size of the throttle body, intake ports and airflow sensor (eg the air flow meter on our cars). A venturi effect also can be a great help to push air faster into the engine. A good example of this would be the velocity stack in the 993's airbox.

Porsche-O-Phile

You have to also consider that if you actually "cram more air" into a volume, you're raising the pressure. As pressure rises, so does temperature. As such, compressive heating will partially offset any benefit. This is why turbo cars have intercoolers and why turbos get so hot.

schumi

If you go to the thread I started "pics of my ride" below, you can see a discussion about the aftermarket fiberglas vented nose panel I have that is open directly to the air filter on my car (which has an S2 intake).